The Antlia Sii 3nm Pro Highspeed filters are specially optimised for fast telescopes with focal ratios between f/2.6 and f/3.6. By pre-shifting the center wavelength, these filters deliver significantly better signal-to-noise ratio (SNR) than the standard 3nm Pro series when used with high-speed imaging systems.

In fast optical systems, light enters the filter at steeper angles due to the cone-shaped light path, which causes the filter’s center wavelength to shift toward the blue end of the spectrum—a phenomenon known as blue shift. At f/2.6, the angle of incidence reaches around 10°, resulting in a bandwidth shift of approximately 2.2nm.

To counter this, Antlia pre-shifted the Highspeed 3nm Pro filters by 1.2nm toward the red end. This compensation ensures optimal transmission and high signal acquisition even under steep light angles, making these filters ideal for capturing narrowband data with fast telescopes.

Application and Performance:

• Over 90% transmittance on the Sulphur II line with a 3nm bandwidth for maximum contrast

• Optimised for fast systems (f/2.6 to f/3.6) with minimal signal loss

• Precision 3nm filter with steep cut-off to reduce halos around bright stars

• Out-of-band blocking rated at OD5 (0.001%) for excellent SNR and minimal interference from unwanted wavelengths

• Built with a single, non-glued optical substrate to eliminate internal reflections

• Ideal for narrowband targets: Emission Nebulae, Planetary Nebulae, Wolf-Rayet Nebulae, and Supernova Remnants

• Suitable for use in both light-polluted and dark-sky locations

• Allows continued imaging even during moonlit nights

• All unmounted Highspeed filters are edge-blackened to suppress stray light reflections

• Superior optical reliability reduces the need for post-processing corrections

• Substrate: Optical-grade, single substrate (non-glued)

• Surface Quality: 60/40 scratch/dig (per MIL-O-13830 standard)

• Transmitted Wavefront Accuracy: λ/4 or better

• Parallelism tolerance: Less than 30 arcseconds

• Warranty: 3 years against delamination

Not recommended for:

• Solar imaging

• Visual observation at night